The assignee of the present invention manufactures and deploys spacecraft for, inter alia, communications and broadcast services. Market demands for such spacecraft have imposed increasingly stringent requirements on spacecraft payload operational capacity. Consequently, such spacecraft may utilize large-area solar panel arrays.
One solar panel technology that may be used in such solar panel arrays is rollable solar panel technology. FIG. 1 depicts a simplified isometric view of a rollable solar panel unit 114. Rollable solar panel unit 114 typically includes a rollable solar panel 111 that may consist of a flexible substrate on which a number of thin film solar cells may be disposed. Rollable solar panel 111 may be wound around a deployment spool 115. Such rollable solar panels may, as illustrated, have a long, thin rectangular shape with opposing short edges and opposing long edges orthogonal to the opposing short edges. The short edges may be substantially parallel to the deployment spool 115 center axis. One short edge may be connected with the deployment spool 115, and the opposing short edge may be proximate to, or connected with, a mounting frame 107. The long edges may be connected with collapsible stiffening members 101, e.g., composite tube sections, that connect the deployment spool 115 with the mounting frame 107. The collapsible stiffening members 101 may be flattened or collapsed, such as is visible in collapsing segment 105, when wound around stiffener winding areas 113 of the deployment spool 115. Similarly, the rollable solar panel 111 may be wound around a solar cell winding area 117 of the deployment spool 115. To deploy the rollable solar panel 111, the deployment spool 115 may be rotated to unwind the rollable solar panel 111 and the collapsible stiffening members 101. The collapsible stiffening members 101, once free of the deployment spool, may revert to their un-collapsed states, such as shown in un-collapsed segment 103, and provide a stiff framework for supporting the unwound flexible solar panel. Typically, the mounting frame 107 will remain stationary and the deployment spool 115 will rotate and move away from the mounting frame 107 as the rollable solar panel 111 deploys.
Large solar panels may thus be packaged in a relatively small space. For example, a rollable solar panel with a deployed size of approximately 16 ft by 92 ft may, in a stowed state, occupy a volume substantially corresponding to a 2 ft diameter cylinder approximately 16 ft in length. Examples of such rollable solar panel technology may be found in U.S. Pat. No. 8,109,472 to Keller et al. Rollable solar panels, while providing a compact stowed configuration and potentially very large photovoltaic areas when deployed, may be generally incapable of providing solar photovoltaic power until after the rollable solar panel is actually deployed.
Rollable solar panels may require support structures that space the rollable solar panels off from the exterior surfaces of a spacecraft and that orient the rollable solar panels once deployed. Such support structures may include booms or other foldable structures. Existing boom structures, such as booms that generally unfold along a single axis away from the spacecraft, e.g., along the pitch axis of the spacecraft, may generate large moments of inertia about the spacecraft center of gravity and may exhibit undesirable amounts of bending along that axis. One such deployment structure is shown in FIG. 2, which depicts a spacecraft with uniaxial boom structures supporting rollable solar panels. The spacecraft 200 may have a main body 252 and two extensible solar arrays 202 that each include a yoke segment 210 and four array segments 212. Two rollable solar arrays 214 may be attached to each array segment 212. The yoke segment 210 and the array segments 212 may all deploy along the pitch axis of the spacecraft 200. In a stowed configuration, the rollable solar panels 214 may be rolled up, and the yoke segment 210 and the array segments 212 may be folded up against the main body 252 in a concertinaed fashion. As a result, the un-deployed arrays are substantially incapable of generating solar photovoltaic power.
In view of the foregoing, the present inventor has realized that there is a need for a deployable rollable solar array support structure that provides higher inherent stiffness in a direction along, for example, the pitch axis of the spacecraft coupled with a lower moment of inertia when the rollable solar array support structure is deployed. The present inventor has also realized that there is a need, in some circumstances, for such a structure to facilitate solar power generation when in the stowed configuration.